GNU bug report logs - #70477
tail command does not hang on /dev/random

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ionut Nicula <nicula.iccc <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: tail command does not hang on /dev/random
Date: Fri, 19 Apr 2024 21:40:35 +0300

The following command hangs indefinitely, as expected:

        tail -c 4096 /dev/random

The following command immediately returns 4097 bytes, unexpectedly:

        tail -c 4097 /dev/random

Details:
- Source code obtained from: git://git.sv.gnu.org/coreutils
- Commit id: 9ab1f9db94479eca4dd2c29b4e21550ff2bcd5bb
- System:

        $ uname -a
        Linux zinc 6.1.0-20-amd64 #1 SMP PREEMPT_DYNAMIC Debian
6.1.85-1 (2024-04-11) x86_64 GNU/Linux

Message #10 received at 70477-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ionut Nicula <nicula.iccc <at> gmail.com>
Cc: 70477-done <at> debbugs.gnu.org
Subject: Re: bug#70477: tail command does not hang on /dev/random
Date: Fri, 19 Apr 2024 21:52:20 -0700

[Message part 1 (text/plain, inline)]

On 2024-04-19 11:40, Ionut Nicula wrote:
> The following command hangs indefinitely, as expected:
> 
>          tail -c 4096 /dev/random
> 
> The following command immediately returns 4097 bytes, unexpectedly:
> 
>          tail -c 4097 /dev/random

Thanks for the bug report. Although the two commands should behave 
similarly, neither should loop: they should both output the requested 
number of random bytes. Similarly for /dev/zero. I installed the 
attached patch to do that.

[0001-tail-avoid-infloop-with-c-on-dev-zero.patch (text/x-patch, attachment)]

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